The Sigma 10-20mm f/3.5 EX DC HSM is an ultra-wide zoom lens designed for crop-frame Pentax cameras. Key features include:

Ultra-Wide Zoom. The Sigma 10-20mm f/3.5 DC HSM for Pentax provides a viewing angle up to 102° while offering a constant f/3.5 aperture throughout its zoom range.

High-Quality Optics. This lens has all the bells and whistles you’d expect, including an HSM motor for rapid and quick autofocus, internal focusing with no front-element rotation, two Extra Low Dispersion elements, one Special Low Dispersion element, and four aspherical lenses to eliminate chromatic aberration and provide very sharp results.